Mitochondrial DNA mutations in Korean patients with Leber’s hereditary optic neuropathy

In order to explore the spectrum of mitochondrial DNA (mtDNA) mutations in Korean patients with Leber's hereditary optic neuropathy (LHON), we investigated the spectrum of mtDNA mutations in 145 Korean probands confirmed with the diagnosis of LHON. Total genomic DNA was isolated from the peripheral blood leukocytes of the patients with suspected LHON, and mtDNA mutations were identified by direct sequencing. Analysis of mtDNA mutations revealed seven primary LHON mutations including the nucleotide positions (nps) 11778A (101 probands, 69.2%), 14484C (31 probands, 21.2%), 3460A (5 probands, 3.4%), and G3635A, G3733A, C4171A, and G13051A mutations in one proband each. In addition, two provisional mtDNA mutations at nps T3472C, and G13259A were each found in one proband, respectively. Another provisional mtDNA mutation at np T3394C was found in two probands. In conclusion, the spectrum of mtDNA mutations in Korean patients with LHON may differ from other ethnicities, which is characterized by high prevalence of 11778A and 14484C mutations, and a low prevalence of the 3460A mutation.


Discussion
In this study, we found seven primary mutations of LHON: Three major primary mutations of 11778A, 14484C and 3460A in 69.2%, 21.4%, and 3.4%, respectively, and 4 additional primary mutations of G3635A, G3733A, C4171A, and G13051A in one proband each.In addition, two provisional mtDNA mutations at nps T3472C and G13259A were each found in one proband, respectively.Another provisional mtDNA mutation at np T3394C was found in two probands.The 11778A mutation is the most common type of LHON mutation worldwide except for the French Canadians.The frequency of 11778A mutation varies among different ethnic groups (Table 2).6][7][8][9] .In Asians, 11778A mutation was found in 85 to 100% of Indian LHON pedigrees, [10][11][12] 86 to 92% of Chinese, 13,14 and 82 to 87% of Japanese [15][16][17]22 . In oreans, two previous reports reported 11778A mutation in 76 to 87% 18,19 .Meanwhile, in the present study, we found 11778A mutation in 69% which is the lowest reported incidence among Asian pedigrees.
In conclusion, the spectrum of mtDNA mutations in Korean patients with LHON is characterized by high prevalence of 11778A and 14484C mutations, and a low prevalence of the 3460A mutation, showing the difference from other ethnicities.Further studies to reveal unidentified pathogenic mitochondrial mutations may provide a better insight into the spectrum for LHON mutations in diverse ethnic groups.

Patients
A retrospective review of mtDNA analyses was performed on 145 consecutive pedigrees in whom mtDNA mutations associated with LHON were found at Seoul National University Bundang Hospital between 2003 and 2023.Informed consent for a genetic test was obtained from all of the patients and/or their legal guardians.The study protocol adhered to the tenets of the Declaration of Helsinki and was approved by the Institutional Review Board of Seoul National University Bundang Hospital (B-1908-558-005).A screening test was performed for the three major LHON primary mutations at nps 3460A/ND1, 11778A/ND4, and 14484C/ND6 in patients who fulfilled the following criteria of (1), (2) and one of (3a-c): (1) history of acute or subacute simultaneous or sequential bilateral optic neuropathy without ocular pain, (2) central scotoma, (3a) maternal history of optic neuropathy, (3b) telangiectatic microangiopathy of the optic disc, and (3c) no response to treatment with corticosteroids.All other causes of optic neuropathy were excluded by ophthalmological and neurological examinations.Some patients underwent additional whole mtDNA analyses as well as orbit and brain magnetic resonance imaging.

DNA analyses
Total mtDNA was extracted from peripheral blood leukocytes using the standard method.Diagnostic restriction site gain or loss was confirmed by direct sequencing using Thermo Sequenase radio-labeled terminator cycle sequencing kits (Amersham, Buckinghamshire, UK) and 6% polyacrylamide sequencing gels.

Table 1 .
Analysis of mitochondrial DNA mutations in 145 Korean probands with Leber's hereditary optic neuropathy.MT-ND mitochondrial encoded NADH dehydrogenase.